Fans are hoping Denji learns to control the Pochita monster inside him as the Chainsaw Man anime progresses. Since he is just 16 years old, he is being used by Japan's Public Safety Unit to slay other demons. Of course, he's all in since he gets paid and enjoys using this as a tool for devastation. Of course, being able to hit on players like Makima and Power is a huge perk.
Denji still has weaknesses since he wields his dog's strength similarly to Naruto and Kurama. It finds out that in order to use chakra, similar to how Naruto and Boruto do, he has to have blood in his system. But even if Denji might feel secure in not becoming a monster in the field, doing so is actually better for his health, nodding to how the Naruto-verse uses its Sage Mode.
Monster Form of Denji Feeds Blood to Him
When Denji and Hayakawa's crew battle the Eternity Devil in a Japanese hotel, Denji activates his chainsaw mode and jumps into the belly of the stonking beast -- literally. He starts cutting it up, hoping to get to its heart, but he loses a lot of blood. This renders him weak, making him vulnerable enough to be killed.
However, his peers realize the more he maims the beast up, he gets to feed on the blood and replenish. This re-energizes him, making the vicious cycle of murder inside the demon's body count. Thus, while the Eternity Devil keeps regenerating, Denji gets stronger too. He's then able to find the heart and end the villain, although he still ends up tired and asleep afterward as he didn't juice up on his own blood. Still, it validates his bloodlust and explains why he needs to keep rampaging when he's let out by the agents.
Denji's Power-Up Requires Him to Continue Killing
Chainsaw Man provides a nice shortcut by allowing Denji to kill more and feed on the devils he fights in the field, essentially using them as a battery. It's akin to Naruto's Sage Mode where ninjas just use nature as a near-infinite energy source. This makes them stronger, with the likes of Jiraiya and Naruto coming close to being shinobi gods in battle.
But in Denji's case, he has to extract this blood from nature, in a sense, like a natural resource. As much as going berserker can make him open to being killed in the field, it allows him to go directly for the source of energy he desperately needs. And ultimately, the more Denji slays, the more he can top up, perfecting how long he lasts in the field. This might help him to access more power and techniques -- the same way Sage Mode upgrades folks' shinobi techniques -- leaving Chainsaw Man fans eager to see how Denji continues to evolve.